It is, of course, a typical 'how far' question.
Remember how you tackle those:
1. Arguments which support the proposition.
2. 'On the other hand it might be said' + argument which support the counter-proposition.
3. A conclusion which weighs the two sides and comes to a decision, using a 'telling point'.

So, paragraph 1.
Start: 'On the one hand, it might be argued that Gorbachev DID cause the collapse of communism.
Then explain + facts all the ways that Gorbachev helped to cause the collapse.
Remember that it's not just enough to talk about the Sinatra Doctrine, glasnost and perestroika etc. - you need to PEE your paragraphs to explain HOW these help bring about the collapse of communism.

Then, paragraph 2.
Start: 'On the other hand, it count be pointed out that Gorbachev did not cause the collapse of communism on his own.
And at this point you need to mention all those other factors which helped the collapse of communism - Afghanistan, the Soviet economy (inc Chernobyl), communist party corruption, the Armenian jokes etc.
Again, it's not enough just to mention them, you need to PEE your paragraphs to explain HOW these help bring about the collapse of communism.

And the conclusion:
Start: 'Therefore...'
Weigh the two sides, and come to a solution.
It's usually a good idea to keep back the best point from the first two paragraphs so you introduce/PEE it here to 'clinch the argument'.